Method for dispersing an immiscible pigment in viscose solution



Aug. 25, 1953 P. VAN DlJK ETAL ,650,168 METHOD FOR DISPERSING ANIMMISCIBLE PIGMENT IN VISCOSE SOLUTION Filed Sept. 1, 1949 FRESH V/scaseARGE ZONE a VISCOSE l A TTOR/VE Patented Aug. 25, 1953 METHOD FORDIS?ERSING AN IMMISCIBLE PIGMENT IN VISCOSE SOLUTION Pieter van Dijk,Velp, and Hans Alwin Schrenk, Arnhem, Netherlands, assignors to AmericanEnka Corporation, Enka, N. 0., a corporation of Delaware ApplicationSeptember 1, 1949, Serial No. 113,622 In the Netherlands October 18,1948 2 Claims.

The present invention relates to a method for uniformly distributing animmiscible pigment in a viscous solution whereby the solution can beextruded to form filamentous threads, fibers, and the like havinguniformly modified characteristics.

It is known according to Dutch Patent No. 21,749 to mix liquid or solidsubstances in spinning solutions by adding them in the feed lines to thespinning machines. This mixture is passed through finely perforatedplates and thence to a tank which may be formed by increasing thecross-section in the feed line. This tank is provided with a mixingdevice of the impeller type which rotates at a sufficiently high rate ofspeed to effect a thorough dispersion. The substance to be added may befirst mixed with a small quantity of the original spinning solution andthis mixture introduced into the feed lines. However, this process hascertain objections particularly in the case of substances that aredifficult to suspend in a finely divided state.

Another conventional method of mixing the substances with spinningsolutions is to circulate the same through a pipe system and maintainthe rate of circulation higher than the rate at which it is dischargedso that a certain amount of the circulating mixture is always contactinga fresh supply of the solution containing the additive agent. (See U. S.Patent No. 2,136,201 and Dutch Patent No. 18,311.) Although thiscirculation has a favorable influence on the distribution, it is notentirely satisfactory to produce a uniform suspension and thereby an endproduct of the desired characteristics.

It is therefore an object of the present invention to provide animproved process whereby immiscible pigments can be continuouslyintroduced into a viscous spinning solution and distributed uniformlythroughout the said solution in a confined mixing zone, and a portion ofthe mixture then drawn off continuously from said zone.

It is another object of the invention to uniformly disperse immisciblepigments in viscous spinning solutions by circulating a spinningsolution containing a suspended substance through a confined mixing zonewhich consists of a primary and an overlapping secondary ring main, therate of circulation in the secondary ring main being substantiallyhigher than in the primary ring main and the direction of circulation inthe zone of overlap being opposite to the direction of circulation inthe remainder of the primary ring main.

Other objects and advantages of this invention will be apparent uponconsideration of the following detailed description when considered inconjunction with the accompanying drawing, wherein the single figurerepresents a diagrammatic form of an apparatus that can be successfullyused for carrying out the process. In

the following description it will be noted that the drawing is veryschematic in view of the fact that the pipe lines, gear pumps, etc., areof the conventional type and it is their particular arrangement andco-action that comprise the present invention. Whereas the same systemcan be successfully employed for modifying the characteristics ofvarious types of viscose solutions by adding the required immisciblesubstances, the description of the drawing will be confined to thepreparation of a viscose-carbon black mixture for the production ofso-called black, spun dyed viscose rayon yarn.

Referring to the drawing, the numerals l, 2, 3, l and 5 indicate branchlines for conducting a viscose-carbon black mixture to a spinningmachine (not shown) by means of spinning pumps 6, 7, 8, 9 and 10. Thebranch lines are fed from a primary ring main H, and the circulation ofthe mixture is effected by means of a gear pump i2. Fresh viscosecontaining no carbon black is conducted from a source, not shown,through a conduit 13 into the primary ring main H. A concentratedsuspension of carbon black in viscose is prepared in an auxiliary tank14 from which the suspension passes through conduit i5 and is forcedinto the primary ring main by means of gear pump 16 at a point betweenthe primary ring main circulating pump [2 and the junction of viscoseconduit l3 and primary ring main H.

A secondary or auxiliary mixing ring main i1 is provided between thepump [2 and the branch lines I, 2, 3, 4 and 5. Gear pump ill in thesecondary ring main i1 forces the viscose in the direction shown by thearrows, viz., in a counter-clockwise direction, so that the flow throughthat portion of primary ring main 1 I, which overlaps or is common toboth the primary and secondary ring, is in the opposite direction to theflow in the remainder of the primary ring main II. (For the direction offlow of the mixture, see the arrows in both the primary and secondaryring mains.)

It will be seen from the above that the apparatus according to theinvention generally consists of a primary ring main provided with theproper connections for supplying the viscous liquid and the substancesto be added, discharge lines to the spinning machine and a pump forcirculating the mixture. The apparatus is specifically characterized byat least one auxiliary or secondary ring main provided with acirculation pump and connected to the primary ring main.

It is an important part of the invention that the flow of the liquid inthat part of the line which coincides with the primary ring main, isopposite to the direction of fiow in the remaining part of the primaryring main. Furthermore, according to the process the rate of flow of themixture to the spinning machine through the branch lines is lower thanthe rate of circulation through the primary ring main, and in turn therate of circulation in the primary ring main is lower than the rate ofcirculation of the mixture in the auxiliary ring line. For example, theflow through the primary ring main should be at least twice as high asthe quantity of spinning solution consumed by the spinning machine, andthe flow through the auxiliary line should be at least four times ashigh as the quantity consumed by the spinning machine. In the practicalapplication of the process it has been found particularly suitable toeffect a flow through the auxilary ring line 5 or 6 times higher thanthat of the flow through the primary main. The combined effect of theopposite direction of flow and the relatively higher rate of circulationin the secondary main is to cause the Well mixed spinning solution tocommingle with the partially mixed spinning solution to produce a veryuniform distribution of the substance within the liquid.

The point Where the pipes 13 and I5 come together and from that pointdownstream through the pump I2 may be regarded as an input zone for thematerial to be mixed. That material flows, as indicated by the arrows,through the pump [8 and straight through the point Q to a point ofdivision P. From the point P some of the material goes to the dischargezone and the remainder is recycled through point Q all as indicated byarrows in the drawing.

Although the circulating pumps are preferably of the positivedisplacement type, such as a gear pump, other types of pumps may beemployed for the same purpose.

In many instances it is desirable to control the temperature of themixture circulating through the pipe system, because many spinningsolutions are susceptible to heat change. Accordingly, this inventionlends itself particularly well to such temperature control, for meanscan be provided for heating or cooling of the liquid in the secondaryring main, which is preferably constructed from small size piping. This,plus the circulation of the liquid at high velocities, is conducive togood heat exchange.

The invention is applicable to all types of processes in whichimmiscible substances are to be uniformly distributed through the bodyof spinning solutions such as viscose, cellulose acetate, casein,artificial resins, etc., and in wet as Well as in dry spinning.

Many types of substances are suitable for use in the process, e. g.,those which are already finely divided, or which can be finely divided,in the form of an emulsion. However, the invention is particularlysuitable for the addition of those types of substances which do not formstable mixtures and which are difficult to distribute evenly in a finelydivided state.

Among these types of substances are th pigments such as titaniumdioxide, carbon black (particularly ga black), pigment-like organicnitrogen compounds for animalizing the solution, emulsifiable substancessuch as oils, for example, liquid paraffin, fats, fat and oilderivatives, artificial resins, particularly in the form ofpolymerisation or condensation products, natural resins, latex, soaps,etc. In the case of adding solid substances such as the pigments, it isoften desirable to suspend or emulsify them in a small quantity of theoriginal spinning solution, and sometimes it is necessary to add anemulsifying or dispersing agent to facilitate the pre-mixing. Thepre-mix can then be introduced into the sys- '4 tern herein disclosed byadding it to the auxiliary tank [4.

The following example will serve to illustrate one mode of operation ofthis system to produce a spinning solution of viscose-carbon black.

ExampZe.The total consumption of viscosecarbon black mixture wasadjusted at V cc. per minute, and the rate of circulation in the primaryring main was adjusted to 4 V cc., while that in the secondary ring mainwas adjusted to 1'7 to 2 V cc. per minute. In the pre-mixing tank,viscose and carbon black were mixed in such a proportion that about 30of carbon black, based on the weight of the cellulose, was suspended inthe viscose, and was supplied to the primary ring main in apredetermined quantity to bring the carbon black content to about 2.4%in the spinning solution that was supplied to the spinning machine. Theviscose mixture obtained in this manner was extremely'homogeneous andsamples of the rayon spun from this mixture exhibited no colordifferences.

The quantitie given above are only by way of illustration, as it isclear that in the practical operation of the system, changes can be madewithout departing from the spirit and scope of the invention.

What is claimed is:

1. A process for uniformly dispersing an immiscible pigment in a viscosesolution which comprises continuously introducing viscose and pigmentinto an input zone, continuously delivering the mixture from the inputzone to a discharge zone, continuously withdrawing a portion of saidviscose-pigment mixture from said discharge zone, continuously returningthe remaining portion from said discharge zone to the input zone, andduring the delivery of said mixture from said input zone to saiddischarge zone, increasing the homogeneity of said mixture by dividingthe flow of mixture at a point downstream from the input zone andupstream from the discharge zone into two streams, and returning one ofsaid streams to a point upstream from the point of division butdownstream from the input zone.

2. A process for uniformly dispersing immiscible pigment in a viscosesolution which comprises continuously introducing viscose and pigmentinto an input zone, continuously delivering the mixture from the inputzone to a discharge zone, continuously withdrawing a portion of saidviscose-pigment mixture from said discharge zone, continuously returningthe remaining portion from said discharge zone to the input zone, andduring the delivery of said mixture from said input zone to saiddischarge zone, increasin the homogeneity of said mixture by dividingthe flow of mixture at a point downstream from the input zone andupstream from the discharge zone into two streams, and returning one ofsaid streams to a point upstream from the point of division at a rate offlow greater than the rate of fiow of the mixture from the input zone tothe discharge zone.

PIETER VAN DIJ K. HANS ALWIN SCI-IRENK.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,039,708 Crouch May 5, 1936' 2,105,684 Costa Jan. 18, 19382,136,201 Whitehead Nov. 8, 1938

1. A PROCESS FOR UNIFORMLY DISPERSING AN IMMISCIBLE PIGMENT IN A VISCOSESOLUTION WHICH COMPRISES CONTINUOUSLY INTRODUCING VISCOSE AND PIGMENTINTO AN INPUT ZONE, CONTINUOUSLY DELIVERING THE MIXTURE FROM THE INPUTZONE TO A DISCHARGE ZONE, CONTINUOUSLY WITHDRAWING A PORTION OF SAIDVISCOSE-PIGMENT MIXTURE FROM SAID DISCHARGE ZONE, CONTINUOUSLY RETURNINGTHE REMAINING PORTION FROM SAID DISCHANGE ZONE TO THE INPUT ZONE, ANDDURING THE DELIVERY OF SAID MIXTURE FROM SAID INPUT ZONE TO SAIDDISCHARGE ZONE INTO HOMOGENEITY OF SAID MIXTURE BY DIVIDING THE FLOW OFMIXTURE AT A POINT DOWNSTREAM FROM THE INPUT ZONE AND UPSTREAM FROM THEDISCHARGE ZONE INTO TWO STREAMS, AND RETURNING ONE OF SAID STREAMS TO APOINT UPSTREAM FROM THE POINT OF DIVISION BUT DOWNSTREAM FROM THE INPUTZONE.